1. Field of the Invention
The present invention relates to remote high-resolution imaging, and specifically to a system and method for forming high-resolution optical and RF images using a differential synthetic aperture radar technique.
2. State of Technology
Synthetic Aperture Radars (SARs) are used in military and non-military applications to provide high-resolution images using a predetermined frequency of electromagnetic radiation. Their spatial resolution is approximately given by the ratio of the wavelength and the effective antenna size. By forming a synthetic aperture, along the direction of flight, much larger than the physical size of the antenna, greatly improved resolution can be obtained along that direction. This is most commonly achieved by generating a profile of target return phase versus position along the synthetic aperture, at spacings equal to about half the physical antenna size (Nyquist rate) or less, while maintaining a linear trajectory.
A normal operating mode of SAR, called Stripmap mode SAR, includes imaging a strip having a length determined by the synthetic aperture as it is flown by a moving platform over a target area. The antenna pointing direction is kept fixed while image data are collected. The length of the strip is determined by a time window over which back-scattered radiation is collected using a series of pulses from an illuminated target area. The collected radiation is processed and an accumulation of data is used to construct a synthesized image of a target area. To form images, the platform is required to fly in a straight line or, if not, deviations from a straight line require corrections during processing.
Another mode of operation, i.e., Spotlight SAR, includes imaging a target by directing an antenna at the center of the imaging scene during the entire pass of the platform to provide a longer illumination time, (i.e., a spotlight aperture).
Accordingly, the present invention provides a Differential Synthetic Aperture Radar imaging technique that reduces system platform constraints to produce higher resolution images.